1. Technical Field
The present disclosure relates to a light-emitting diode, and more particularly, to a light-emitting diode having a low contact resistance layer.
2. Description of Related Art
A light-emitting diode (LED) is generally formed an epitaxy structure on an insulation substrate, wherein the epitaxy structure includes a P-type metal electrode, a P-type semiconductor layer, a light-emitting layer, an N-type semiconductor layer, and an N-type metal electrode. In the LED, the insulation substrate may be sapphire. Since it is required for the P-type metal electrode and the N-type metal electrode of the LED to be formed on the same surface of the insulation layer, the current crowding easily occurs on the surface and decreases the light-emitting efficiency of the LED, so as to degrade the operation potential of the LED.
FIG. 1 is shown a cross-sectional view of a conventional light-emitting diode (LED) 100. The LED 100 includes a substrate 110, an N-type semiconductor layer 120, a light-emitting layer 130, a P-type semiconductor layer 140, a P-type metal electrode 150 and an N-type metal electrode 160. In FIG. 1, current 170 starts from the P-type metal electrode 150, and goes through the P-type semiconductor layer 140, the light-emitting layer 130 and the N-type semiconductor layer 120 to reach the N-type metal electrode 160. Since the current 170 always goes a pathway of the lowest resistance, the current crowding is apt to generate near the P-type metal electrode 150 or the N-type metal electrode 160, which decreases the light-emitting efficiency of the LED 100. As shown in FIG. 1, the current crowding occurs near the N-type metal electrode 160.
FIG. 2 is shown a cross-sectional view of a conventional LED 200 and a schematic view of a current pathway in the LED 200. The LED 200 includes a substrate 210, an N-type semiconductor layer 220, a light-emitting layer 230, a P-type semiconductor layer 240, a transparent conductive layer 250, a P-type metal electrode 260 and an N-type metal electrode 270. In FIG. 2, if the resistance of the transparent conductive layer 250 is far less than the resistance of the N-type semiconductor layer 220, the current may follow the pathway A, from the P-type metal electrode 260 to the N-type metal electrode 270, and then the current crowding occurs near the N-type metal electrode 270. If the resistance of the N-type semiconductor layer 220 is far less than the resistance of the transparent conductive layer 250, the current may follow the pathway B, from the P-type metal electrode 260 to the N-type metal electrode 270, and then the current crowding occurs near the P-type metal electrode 260.
Due to the occurrence of the current crowding, the conventional LED has higher operation potential at the P-type metal electrode or the N-type metal electrode. And in an LED, such uneven distribution of current may cause uneven distribution in color, premature saturation of light intensity, and insufficient reliability of electrical elements. Therefore, an improved LED and a method of manufacturing the same are needed to solve the aforementioned problems.